A radiation image conversion panel in which a stimulable phosphor layer is provided on a substrate has been developed in order to produce a radiation image obtained without using a silver halide.
A radiation energy depending on a radiation transmittance density on each part of the object can be accumulated through the radiation image conversion panel by irradiating a radiation that has been transmitted through an object to a stimulable phosphor. The radiation energy accumulated in a stimulable phosphor is subsequently emitted as a stimulated luminescence by irradiating the stimulable phosphor with electromagnetic waves (stimulating light) such as visible light and infrared radiation to excite on a time series basis. This signal based on light intensity can be reproduced as a visible image on a recording material such as a silver halide photographic sensitized material and a display apparatus such as CRT by converting this signal into an electric signal by, for example, photoelectric conversion.
It is well known that the superiority or inferiority of the radiation image conversion system using the radiation image conversion panel, is largely controlled by luminance of the stimulated luminescence of the panel and the luminescence uniformity of the panel, and particularly, these characteristics are largely influenced by the characteristic of the stimulable phosphor to be used.
It is described in Patent document 1 that a radiation image conversion panel with high luminance can be obtained by using a stimulable phosphor as expressed in the following formula (1);M1X.aM2X′2.bM3X″3:eA  (1)where M1 represents at least one alkali metal selected from the group including Li, Na, K, Rb and Cs; M2 represents at least one divalent metal selected from the group including Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni; M3 represents at least one trivalent metal selected from the group including Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In; each of X, X′ and X″ represents at least one halogen selected from the group including F, Cl, Br and I; A represents at least one metal selected from the group including Eu, Tb, In, Ga, Cs, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and Mg; and a, b and e respectively show numerical values within ranges of 0≦a<0.5, 0≦b<0.5 and 0.001<e≦1.0.
An experiment by which columnar crystals composed of a stimulable phosphor are formed on a support with a vapor deposition method has also been made (Refer to Patent document 1).
Sharpness of an image obtained from a radiation image conversion panel having such a structure can be enhanced since a stimulating light which enters the inside of columnar crystals from the surface of a stimulable phosphor layer is totally reflected on the side of columnar crystals, and then travels up to the surface of the stimulable phosphor layer, without being diffused.
But, it is known that sharpness is degraded because the stimulating light which enters a space between columnar crystals is scattered and diffused on the side of columnar crystals. In order to avoid this, filling of a filler such as a high light absorbance material or a high light reflectance material in the spacing between columnar crystals has been tried (Refer to Patent document 1).
[Patent document 1] Japanese Patent O.P.I. Publication No. 2003-248097